Electrolytic alkali-chlorine diaphragm cell



Feb. 20, 1962 c. P. LE BLANC ET A1. 3,022,244

ELECTROLYTIC ALKALI-CHLORINE DIAPHRAGM CELL Filed June 26, 1959 FIG. 2

A frog/M6121 United vStates Patent' 3,022,244 ELECTROLYTIC ALKALI-CHLOPJNE DIAPHRAGM CELL Carrol P. Le Blanc, Maplewood, and Lewis W..Henslee,

Jr., Lake Charles, La., assignors, by mesne assignments,

to Pittsburgh Plate Glass Company Filed June 26, 1959, Ser. No. 823,025 2 Claims. (Cl. 204-266) This invention relates to a novel type of electrolytic cell such as suitable for production of alkali metal hydroxide and elemental chlorine, and also to the diaphragms used in such cells. It is known that chlorine and aqueous alkali metal hydroxide can be produced readily by electrolysis of alkali metal chloride brine in a diaphragm type cell. Such a cell consists essentially of a cell enclosure and an anode of chlorine-resistant electroconductive material, such as carbon, platinum or platinum coated titanium or the like, and a foraminous cathode, usually made of iron, within the enclosure. The anode and cathode are separated by means of a porous diaphragm of asbestos or like material, thus providing an anode compartment and a cathode compartment.

In the normal construction of such cells, the diaphragm is in direct contact with the cathode. Frequently, the diaphragm is deposited on the cathode by placing the cathode in an aqueous slurry of asbestos and causing the slurry to tlow through the pores or mesh openings of the cathode until a porous sheet or layer of asbestos has been deposited upon the side of the cathode which in use is opposite the anode.

In operation of such a cell, the cell is filled with brine and an electrical potential is established between the anode and cathode. Chlorine is evolved at the anode and is Withdrawn from the cell at a point above the liquid level in the anode compartment. Brine is fed into the anode compartment at a substantially continuous rate and the electrolyte flows through the pores of the diaphragm and through the cathode. In the course of this flow, alkali metal hydroxide is produced and hydrogen liberated at-the cathode. The hydrogen is withdrawn from the cathode compartment which is behind the cathode at a point above the liquor level therein andv aqueous alkali metal hydroxide is Withdrawn from the cathode compartment at a lower level.

Typical electrolytic cells of this type which have found extensive commercial use are described in United States Letters Patent Nos. 1,862,245, granted .lune 7, 1932, an 1,866,065, granted July 5, 1932.

Cells typical of the type mentioned above are shown in the accompanying drawing in which:

FIGURE l is a side view of an alkali-metal-chlorine electrolytic diaphragm cell partially broken away and in section to show the anodes and cathode therein.

FIGURE 2 is an enlarged view of one of the cathode fingers of such a cell showing the asbestos diaphragm in place and impregnated with carbon particles according to the teachings of this invention.

ln FIGURE 1 is shown an alkali-metal-chlorine electrolytic diaphragm cell having a top 1, a bottom 2, and intermediate cathode carrying section 3. Located at the top of the cell is a chlorine outlet 4 and a brine inlet 5. The cell is provided with a caustic outlet 6 and a hydrogen outlet 7, both of which are in communication with the interior of the cathode. As can be seen in the drawing, specifically FIGURE l, the cell is provided with anode blades 8 and the cathode of the cell is divided into a plurality of cathode lingers 9. The anode blades are embedded in a lead base 10 which is covered with a mastic 11. Current is introduced into the cell through the negative bus bar 13. The conduction of current through the cell is accomplished by introducing the current through 'ieee According to this invention it has been found that electrolytic cells of this character may be operated at lower voltage by use of an asbestos diaphragm in which elemental carbon particles are dispersed more or less uniformly. Such reduction in voltage is quite important since it alfords a reduction in the amount of energy required per ton of chlorine and/or alkali metal hydroxide produced.

The amount of carbon dispersed in the diaphragm is capable of rather wide range of variation from about l to about 60 percent by Weight based upon the dry weight of asbestos therein. The carbon should be pulverulent, usually being below about 60 mesh in particle size. Carbon black of the type used for rubber fillers or reinforcing pigments, powdered graphite, and powdered carbon useful for filter aids or adsorbents, may be used for this purpose. The exact amount to be used depends upon the particle size of the carbon, the size of the asbestos fibers, and the degree of tightness that the fibers are interlaced. Thus, the diaphragm itself should be porous and permit ready flow of brine therethrough under a head of about 4 to 30 inches of saturated NaCl brine. If too much carbon is incorporated, the asbestos remaining is insucient to provide the fibers necessary for a coherent sheet, and the diaphragm will gradually disintegrate in use. IfV too low in concentration, the carbon does not exert a noticeable eect upon the diaphragm and the cell. Usually, the elemental carbon content of the diaphragm is l to 40 percent by Weight of the diaphragm, including the carbon.

The diaphragm herein contemplated may be prepared readily by forming a iluid aqueous slurry of asbestos and elemental carbon particles, immersing the cathode in such a slurry, and flowing the slurry through the pores or meshes of the cathode to deposit a carbon-containing asbestos sheet on the cathode in a manner similar to that normally used for depositing diaphragms on cathodes of alkali-chlorine cells. The diaphragms thus deposited are about yu; to SAG inch in thickness.

Alternatively, asbestos paper may be impregnated with an aqueous slurry of carbon particles and the carbon therein thus occluded or otherwise entrapped in the pores of the paper.

The carbon-containing diaphragm herein contemplated may be used in connection with a wide variety of electrolytic cells, including those disclosed in the above mentioned patents as well as those described in the following United States Letters Patent: 2,282,058, 2,409,912, 2,666,028, 2,681,884, 2,681,887, 2,742,420, 2,858,263, and 2,860,100.

The following examples are illustrative:

Example I A laboratory electrolytie cell was used in these tests. The cathode was in the form of a vertical cylinder about 1% inches in diameter and was made of heavy iron screen. Anode rods depended downardly from the cell cover and were disposed around the cathode, the space between the anode rods and the cathode being about 1/2 inch.

A diaphragm was depended on the outside face of the cathode by forming an aqueous slurry of asbestos and a pulverulent carbon which is normally used as a filter aid and has a particle size such that about 70 percent of this material has a particle size between 325 mesh and 150 mesh. This slurry contained about 1.6 percent by weight of asbestos (being a mixture of 2 parts by weight of short bers, Quebec Asbestos Producers Asso- Vciation, Grade 4T, and l part by Weight of long fibers,

Quebec Asbestos'Producers Association, Grade 3R) and 0.3 percent by weight of the Qcarbon. The cathodewas immersed in the slurry and the asbestos diaphragm deposited on the outside cathode surface by drawing the slurry through the cathode, ultimately establishing a pressure 'drop' between the inside and the outside of the cathode of V28 inches of mercury.

The cell was then assembledr and aqueous sodium chloride brine Ycontaining'. an average of 312 grams of NaCl perliter'was fedV into the anolyte compartment of the cell ata vcmstalat'rate,n evolved chlorine and hydrogen and sodium hydroxide solution being Withdrawn in the conventional manner. The cell was operated at 185 F., with aap'r'essure 'drop between the anolyte and catholyteV Y z of ll inches of water, continuously Vfor 19 days with.

an average current eici'enc'y of 95.5 percent. The average Y VpH of theanolyte Was about 4.2 and the average voltage across the cell was 3.336 volts. The concentration of sodium hydroxide in the solution which was "produced was "121' Vgrains of NaOH per liter of solution.

" "In a control experiment using noY carbon in the asbestos,

Y the'average voltage was 3.609 volts, the other conditions 4 containing on the average 322 grams of NaCl per liter of solution. The average voltageon-these cells was 3.46 volts, about 0.1 volt lower thanthat required with the normal asbestos diaphragm.

Although the present invention has been described with reference to theispecic details of Ycertain embodiments thereof, it is not intended that suchl details shall limit the scope of the invention.

What is claimed:

1. In an electrolytic"alkal1 chlorineV cell having an anode, a foraminous cathode, axporous asbestos diaphragm inthe formrof a porous sheet on the cathode and between `the anode and the cathode, thus providing an anode compartment between the anodeY and the diaphragm, means for feeding brinefinto the anode compartment, means for withdrawing evolvedY chlorine from the anode compartment, and means behind the foraminous cathode for withdrawing evolved hydrogen and alkali metal hydroxide, the improvement wherein the diaphragm Vhas discrete carbon particles disposed within the asbestos diaphragm sheet said sheet having been formed by depositingY the diaphragmon the cathode from an aqueous slurry of asbestos containing 1 to 60 rpercent carbon dispersed therein basis'the dry weight of asbestos. l 2. The apparatus of claim 1 in which the carbon particles are below 16 mesh in size and the diaphragm is between 1A@ to 9A@ inch in thickness. Y f

References cited 111 the fue of this-patent UNITED srArEsrArENrs 1,378,599 Miche1 f f r May 17, 1921 1,982,224 Michel Nov. 27, 1934 'FOREIGN PATENTS 16,437 Great Britain Dee. 13,1884 12,1,242 

1. IN AN ELECTROLYTIC ALKALI CHLORINE CELL HAVING AN ANODE, A FORAMINOUS CATHODE, A POROUS ASBESTORS DIAPHRAGRAM IN THE FORM OF A POROUS SHEET ON THE CATHODE AND BETWEN THE ANODE AND THE CATHODE, THUS PROVIDING AN ANODE COMPARTMENT BETWEEN THE ANODE AND THE DIAPHRAGM, MEANS FOR FEEDING BRINE INTO THE ANODE COMPARTMENT, MEANS FOR WITHDRAWING EVOLVED CHLORINE FROM THE ANODE COMPARTMENT, AND MEANS BEHIND THE FORAMINOUS 